use rustc::hir::*;
use rustc::hir::map::Node::NodeItem;
use rustc::lint::*;
use rustc::ty;
use syntax::ast::LitKind;
use syntax::symbol::InternedString;
use utils::paths;
use utils::{is_expn_of, match_def_path, match_type, resolve_node, span_lint, walk_ptrs_ty};
declare_lint! {
pub USELESS_FORMAT,
Warn,
"useless use of `format!`"
}
#[derive(Copy, Clone, Debug)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array![USELESS_FORMAT]
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let Some(span) = is_expn_of(expr.span, "format") {
match expr.node {
ExprCall(ref fun, ref args) => {
if_let_chain!{[
let ExprPath(ref qpath) = fun.node,
args.len() == 2,
match_def_path(cx.tcx, resolve_node(cx, qpath, fun.id).def_id(), &paths::FMT_ARGUMENTS_NEWV1),
check_static_str(cx, &args[0]),
check_arg_is_display(cx, &args[1])
], {
span_lint(cx, USELESS_FORMAT, span, "useless use of `format!`");
}}
},
ExprMatch(ref matchee, _, _) => {
if let ExprTup(ref tup) = matchee.node {
if tup.is_empty() {
span_lint(cx, USELESS_FORMAT, span, "useless use of `format!`");
}
}
},
_ => (),
}
}
}
}
pub fn get_argument_fmtstr_parts<'a, 'b>(cx: &LateContext<'a, 'b>, expr: &'a Expr) -> Option<Vec<InternedString>> {
if_let_chain! {[
let ExprBlock(ref block) = expr.node,
block.stmts.len() == 1,
let StmtDecl(ref decl, _) = block.stmts[0].node,
let DeclItem(ref decl) = decl.node,
let Some(NodeItem(decl)) = cx.tcx.hir.find(decl.id),
decl.name == "__STATIC_FMTSTR",
let ItemStatic(_, _, ref expr) = decl.node,
let ExprAddrOf(_, ref expr) = cx.tcx.hir.body(*expr).value.node, let ExprArray(ref exprs) = expr.node,
], {
let mut result = Vec::new();
for expr in exprs {
if let ExprLit(ref lit) = expr.node {
if let LitKind::Str(ref lit, _) = lit.node {
result.push(lit.as_str());
}
}
}
return Some(result);
}}
None
}
fn check_static_str(cx: &LateContext, expr: &Expr) -> bool {
if let Some(expr) = get_argument_fmtstr_parts(cx, expr) {
expr.len() == 1 && expr[0].is_empty()
} else {
false
}
}
fn check_arg_is_display(cx: &LateContext, expr: &Expr) -> bool {
if_let_chain! {[
let ExprAddrOf(_, ref expr) = expr.node,
let ExprMatch(_, ref arms, _) = expr.node,
arms.len() == 1,
arms[0].pats.len() == 1,
let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node,
pat.len() == 1,
let ExprArray(ref exprs) = arms[0].body.node,
exprs.len() == 1,
let ExprCall(_, ref args) = exprs[0].node,
args.len() == 2,
let ExprPath(ref qpath) = args[1].node,
match_def_path(cx.tcx, resolve_node(cx, qpath, args[1].id).def_id(), &paths::DISPLAY_FMT_METHOD),
], {
let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0]));
return ty.sty == ty::TyStr || match_type(cx, ty, &paths::STRING);
}}
false
}